1. Field of the Invention
The present invention relates to the field of medical and dental devices, and more particularly to guidewires and stylets used in intra-vascular procedures and arch wires used in orthodontia procedures.
2. Description of the Related Prior Art
A major requirement for medical guidewires and other guiding members, whether they are formed of solid wire or tubular members, is that they have sufficient column strength and stiffness to be pushed through passageways in a patient, such as the patient's vascular system, with minimal kinking or binding. However, the distal section of the guidewire must also be flexible enough to avoid damaging the blood vessel or other body lumen through which it is advanced. Accordingly, efforts have been made to provide guidewires having a favorable combination of both strength and flexibility in order to make them suitable for their intended uses. However, strength for pushing and flexibility for turning without damaging vascular walls tend to be diametrically opposed to one another, such that an increase in one usually involves a decrease in the other, as exemplified below.
The cores of conventional guidewires have been made of many different materials. Two of the more popular materials are stainless steel and Nitinol. In particular, stainless steel has good pushability properties as well as good torque qualities. In turn, guidewire cores formed of such material are generally found suitable for being advanced, and further, for being rotated, so as aid in their being maneuvered, through a patient's vascular system. However, such steel core guidewires tend to be stiff, i.e., not easily bent, and limited in their flexibility. Therefore, the steel guidewire can be found to bind or kink as it is advanced in the vascular anatomy. As is known, once the guidewire is kinked, it must often be discarded and replaced with a new guidewire.
On the other hand, guidewires formed with Nitinol cores are found to have the flexibility that is warranted for negotiation through a tortuous path in a patient's body lumens or vessels. In turn, when being advanced through a patient's vascular system, such guidewires are found to exhibit lower potential for either damaging the patient's vessel/body lumen or kinking/binding. Unfortunately, such Nitinol guidewires are found to be quite soft while exhibiting good shape memory. Accordingly, they are found to have limited pushability against resistance of tortuosity (e.g., in comparison to guidewires having stainless steel cores) because they tend to straighten out or return to their original shape during their advancement. The shape memory can make it difficult for a physician to shape the tip of the guidewire with his fingers for accessing difficult to reach portions of the patient's vascular system.
In light of the above, efforts have been made to blend the favorable characteristics of both stainless steel and Nitinol in guidewires. These efforts have resulted in a variety of differing designs. One widespread wire design involves joining materials of differing properties along the wire's extent. As shown, three materials are sequentially joined in forming the core of the wire: (i) stainless steel used as a proximal portion, (ii) a segment of binary superelastic alloy distally joined to the stainless steel portion (an alloy often utilized is Nitinol), and (iii) a further segment of stainless steel distally joined to the superelastic segment, forming the end of the wire. Due to its stiffness, the proximal portion of stainless steel allows the wire to be pushable over much of its length as it is threaded invivo. However, because the superelastic segment exhibits good kink resistance, it aids the movement of the wire's distal region through the tortuosity of the system in which the wire is being threaded. Finally, the distal stainless steel segment, serving as a shaping ribbon, enables adequate control and shapeability of the wire at its distal end.
However, there are drawbacks to such wire core configurations. First, extreme care and precision are required in joining distinct sections in forming the wire core, which lends itself to significant manufacturing time and cost. Second, potential joint failures along the length of the core represent an ever-present risk during use of the wire. Third, while the use of stainless steel and superelastic materials in the wire core help to exhibit both column strength and kink resistance, respectively, one or more of these properties can generally be found to be impeded when joining separate materials.
Similar to that described above concerning guidewires in the medical field, there are other fields of art that would be well served with wires having a combination of both column strength and kink resistance properties. One example is in the field of dentistry, specifically with respect to arch wires used for orthodontia. Such arch wires need sufficient column strength and stiffness for their use in effectively aligning or straightening teeth, with minimal kinking or binding to the wires. To this end, the arch wires must be flexible enough so as to be routinely reshaped by a dentist as a patient's teeth are aligned over time. Standard binary Nitinol has generally been used as the material of choice for such arch wires because of its good flexibility properties; however, such material is generally lacking in terms of its overall strength and stiffness properties.
What are needed are apparatus and/or systematic methods to address or overcome one or more of the limitations briefly described above with respect to conventional medical wires used for guiding purposes, and which may be further applicable in other fields where such combined wire properties would be considered advantageous, such as with orthodontia wires used for teeth aligning purposes.